Process for Cracking of Waste Oil by Microwave

ABSTRACT

A process and apparatus for heating liquid material, which are particularly suitable for refining waste oil, are disclosed. The process comprises the steps of creating a swirling body of liquid material, such as waste oil, within a reaction chamber, and exposing the swirling body of material to microwave radiation.

This invention relates primarily to the refining of waste oil, and in particular to microwave-activated cracking of waste oil. However, the process and apparatus of the invention may have applications in other fields.

A large proportion of the waste oil generated in the UK is collected and subjected to a rudimentary reprocessing treatment that removes water and solid contaminants to form a recovered fuel oil. The recovered fuel oil is then used as an alternative fuel in power stations, heaters at quarries, cement & lime kilns, and industrial furnaces. However, from 2006, the European Waste Incineration Directive will prevent many of the current users of recovered fuel oil from burning it.

Many attempts have been made to devise a commercially viable process for refining waste oil, but none have been entirely satisfactory. This is because waste oils pose a significant problem due to their variable properties, and high sediment, sulphur and chlorine content. Refining waste oil to base oils is possible and is practised to a certain degree, but presently available products are not accepted as being equivalent to base oil. Consequently, there is a need for a process to refine waste oils to produce hydrocarbon fuels that conform to normal specifications in respect of product quality, and in particular sulphur content.

A current area of research in the field of waste oil refining is concerned with microwave-activated cracking. Typical hydrocarbons do not interact with microwaves because they are non-polar. However, in the presence of appropriate sensitisers, photon absorption takes place that is sufficiently intense for “hot spots” to form that are localised in both space and time. It has been demonstrated that sufficiently high local temperatures and pressures exist for free radical reactions to occur at bulk temperatures well below those required for thermally activated processes.

A satisfactory microwave-activated refining process for waste oil has yet to be developed because of the large amount of heavy material and sediments produced by such a process, and the high temperature of the “hot spots” causing breakages of the microwave conducting materials.

There has now been devised an improved process, and an improved apparatus, which overcome or substantially mitigate the above-mentioned and/or other disadvantages associated with the prior art.

According to a first aspect of the invention, there is provided a process for refining waste oil, the process comprising creating a swirling body of waste oil within a reaction chamber, and exposing the swirling body of waste oil to microwave radiation such that cracking reactions occur.

According to a further aspect of the invention, there is provided an apparatus for refining waste oil, the apparatus comprising a reaction chamber within which, in use, a swirling body of waste oil is created, and a source of microwave radiation adapted to expose the swirling body of waste oil to microwave radiation such that cracking reactions occur.

The process and apparatus according to the invention are advantageous principally because the swirling movement of the body of waste oil within the reaction chamber reduces the risk of the high localised temperatures and pressures created by the microwave radiation damaging the apparatus. In addition, the rotation of the body of waste oil ensures that the waste oil remains in a fluid form when lighter fractions of the waste oil have been removed.

In preferred embodiments, waste oil is transferred from a reservoir tank, either directly into the reaction chamber or more preferably into a circuit conduit that communicates with the reaction chamber, via one or more injection conduits such that a swirling body of waste oil is formed within the reaction chamber. This arrangement is particularly advantageous because there is no need for the apparatus to include a mechanism disposed within the reaction chamber or the circuit conduit that would be liable to restrict the passage of heavy material produced by the cracking reactions, and hence potentially cause a blockage.

Most preferably, a swirling body of waste oil is formed within the circuit conduit, which preferably communicates with an opening in a lower part of the reaction chamber, and this swirling body preferably rises by thermal effects into the reaction chamber. The one or more injection conduits preferably therefore guide the waste oil into a portion of the circuit conduit that is offset from its central, longitudinal axis, along a direction that is orientated transversely to that axis.

In presently preferred embodiments, the reaction chamber is cylindrical, with open upper and lower ends, and is orientated generally vertically. The portion of the circuit conduit that is immediately below the reaction chamber is preferably also orientated vertically, and the injection conduits preferably feed the waste oil into the circuit conduit in a generally horizontal direction. Furthermore, the open lower end of the reaction chamber is preferably in sealed communication with the circuit conduit, and preferably has an internal diameter that matches the internal diameter of the circuit conduit.

At least a portion of the wall, and most preferably the entire wall, of the reaction chamber is preferably formed from a material, such as a heat-resistant glass, that has a high transmittance of microwave electromagnetic radiation.

The waste oil is preferably held within a reservoir tank from which the waste oil is transferred as required to the reaction chamber. As the cracking reactions refine the waste oil and the products are removed, the waste oil is preferably replenished within the reservoir tank so as to maintain the level of waste oil within the reservoir tank substantially constant. Most preferably, the waste oil is heated before being introduced into the reservoir tank, and is heated further within the reservoir tank by conventional means.

A suitable microwave radiation sensitiser is preferably added to the waste oil before it is transferred to the reaction chamber. Most preferably, the sensitiser is added to the waste oil before it is introduced into the reservoir tank. Suitable sensitisers are known in the art. Other additives, such as a catalyst, are also preferably added to the waste oil before it is introduced into the reservoir tank.

Waste oil that cools within the reaction chamber before undergoing any cracking, as well as larger solid sediments, is preferably replaced from below by swirling bodies of waste oil at a higher temperature. The circuit conduit preferably extends from an opening in the lower part of the reaction chamber to a port in a lower portion of the reservoir tank. The cooler waste oil and solid sediments preferably fall, under the action of gravity, along the circuit conduit into the reservoir tank such that there is a continuous flow of waste oil from the reservoir tank, into the circuit conduit, and back into the reservoir tank. This continuous flow maintains the waste oil in the circuit conduit in a fluid state to ensure the continued functioning of the apparatus.

Solid sediments and other heavy materials, such as carbon, metals and catalyst residue, build up in a lower portion of the reservoir tank during use. This heavy material, commonly referred to as tar, is preferably intermittently drained through an outlet port in the base of the reservoir tank in order to ensure that the waste oil within the reservoir tank remains sufficiently fluid to circulate. In order to facilitate draining of the tar, the base of the reservoir tank is preferably tapered, eg generally frusto-conical, in shape. A conventional auger unit may be used to drain this heavy material.

As discussed above, a catalyst may be added to the waste oil before it is introduced into the reservoir tank. Alternatively, or preferably in addition, a catalytic substrate may be situated within the reaction chamber during use.

For instance, the catalytic substrate may comprise carbon as a catalyst. In presently preferred embodiments, the catalytic substrate has the form of a rod that extends along a central axis of the reaction chamber.

The catalytic substrate is preferably mounted at its ends, with the mountings being situated outside the reaction chamber. In presently preferred embodiments, the mountings are situated within inlet and outlet ports for the reaction chamber. In particular, each of the mountings preferably comprises a central hub for receiving an end portion of the catalytic substrate, and a plurality of radial support struts. In the inlet port, the radial support struts preferably have the form of deflector blades, the deflector blades being adapted to deflect waste oil flowing into the reaction chamber transversely relative to the longitudinal axis of the reaction chamber so as to facilitate formation of a swirling body of waste oil.

A microwave barrier is preferably disposed within an outlet port for the reaction chamber, and the microwave barrier preferably comprises one or more electrically conductive members suitable for preventing escape of microwave radiation from the reaction chamber through the outlet port. In presently preferred embodiments, the microwave barrier has the form of a turbine rotor that is caused to rotate by material exiting the reaction chamber through the outlet port. Rotation of the turbine rotor may therefore be monitored, during use, and the rate of flow through the outlet port thereby calculated.

In presently preferred embodiments, the mounting for the catalytic substrate within the outlet port preferably also acts as a mounting for the turbine rotor. The turbine rotor is preferably therefore mounted about the central hub of the mounting.

The reaction chamber is preferably housed within a jacket formed of a material that does not absorb microwave radiation, such as stainless steel or aluminium. In particular, the reaction chamber is preferably mounted co-axially within a cylindrical jacket, with an inert gas-filled space separating the reaction chamber from the wall of the jacket. Microwave radiation preferably enters the jacket through a window, before entering the reaction chamber to be absorbed by the swirling body of waste oil. The window is preferably dimensioned and configured such that the entire reaction chamber is exposed to microwave radiation. A waveguide preferably transmits the microwave radiation from a suitable source to the window of the jacket. The microwave radiation preferably has a frequency at the lower end of the microwave range, eg approximately 1 GHz frequency, and preferably has a power of greater than 30 kW, and most preferably greater than 50 kW.

In preferred embodiments of the apparatus according to the invention the products of the cracking reactions are separated. In particular, the reaction chamber preferably has an upper opening through which vapour products, and also any entrained liquid droplets and solid particles, escape from the reaction chamber. The vapour products, and any entrained liquid droplets and solid particles, passing through the upper opening of the reaction chamber are preferably transferred to an upper portion of the reservoir tank where the entrained liquid droplets and solid particles are returned to the waste oil. The reservoir tank preferably includes an upper outlet port through which the vapour products then flow into a product recovery apparatus. The product recovery apparatus may have any form suitable for cooling and separating the vapour products into useful fractions.

As mentioned above, the process and apparatus of the invention may be useful in applications other than the refining of waste oil. Thus, in its broadest aspects, the present invention provides

(a) a process for heating liquid material, the process comprising creating a swirling body of said material within a reaction chamber, and exposing the swirling body of material to microwave radiation; and

(b) an apparatus for heating liquid material, the apparatus comprising a reaction chamber within which, in use, a swirling body of said material is created, and a source of microwave radiation adapted to exposing the swirling body of material to microwave radiation.

Examples of other fields of application in which the invention may be used are processing of foodstuffs, drying of materials, viscosity reduction of heavy fuel oils, and many others.

The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which

FIG. 1 is a side view, partly cut-away, of apparatus according to the invention;

FIG. 2 is a front view, partly cut-away, of apparatus according to the invention;

FIG. 3 is an exploded view of a reactor that forms part of apparatus according to the invention;

FIG. 4 is a schematic of the reactor connected to peripheral equipment;

FIG. 5 is a schematic cross-sectional view of an alternative reactor for the apparatus of FIGS. 1 to 4;

FIG. 6 is a cross-sectional view along the line VI-VI in FIG. 5;

FIG. 7 is a cross-sectional view along the line VII-VII in FIG. 5; and

FIG. 8 is a cross-sectional view along the line VIII-VIII in FIG. 5.

Apparatus according to the invention is shown in FIGS. 1 and 2. The apparatus comprises a reservoir tank 10 that forms the lower part of a distillation column 20 (only part of which is shown in FIGS. 1 and 2), and three reactors 30. The distillation column 20 is of known form, and is used to separate fractions of the refined oil by distillation. The reservoir tank 10 and reactors 30 are mounted within an appropriate support frame (parts of which are not shown in FIGS. 1 and 2, for clarity) including a standing platform to facilitate maintenance of the apparatus.

The reservoir tank 10 comprises a generally cylindrical main portion, a generally dome-shaped upper portion, and a frusto-conical lower portion. An upper outlet port 11 is formed at the apex of the upper portion of the reservoir tank 10, the remainder of the distillation column 20 extending upwardly therefrom, and a lower outlet port 12 is formed at the base of the reservoir tank 10. The reservoir tank 10 also includes an inlet port (not shown in the Figures) through which pre-heated waste oil, which contains appropriate amounts of a microwave sensitiser and other additives, is supplied to the reservoir tank 10. The reservoir tank 10 also includes means for further pre-heating the waste oil.

A lower circuit port 14 is formed in a side wall of the lower portion of the reservoir tank 10, and an upper circuit port 24 is formed in an upper wall of the upper portion of the reservoir tank 10. As shown most clearly in FIG. 2, the lower circuit port 14 is connected to three lower circuit pipes 15, and the upper circuit port 24 is connected to three upper circuit pipes 25.

Each lower circuit pipe 15 extends generally horizontally away from the reservoir tank 10 and then vertically upwards into connection with an inlet port 32 of one of the reactors 30. Each lower circuit pipe 15 is formed from several components, but has a generally constant internal diameter of approximately 200 mm. Each upper circuit pipe 25 extends generally upwardly and outwardly away from the upper portion of the reservoir tank 10 to a highest point, and then vertically downwards into connection with an outlet port 31 of one of the reactors 30. Each upper circuit pipe 25 is formed from several components, but has a generally constant internal diameter of approximately 80 mm. In addition, the upper circuit pipes 25 each include a viewing window 26 that is formed of a sufficiently transparent material to enable a user to view the interior of the pipe 25. Inlet port 32 and outlet port 31 have inline valves (not shown) fitted, such that maintenance work can be carried out on a reactor 30 without interrupting the flow of oil to other, still functioning reactors 30.

A feed pipe 16 of reduced diameter relative to the upper and lower circuit pipes 15,25 extends horizontally away from a side wall of the lower portion of the reservoir tank 10, above the lower circuit pipe 15, to a variable speed pump 17. From the variable speed pump 17, the feed pipe 16 extends upwardly before dividing into three branches, one for each of the lower circuit pipes 15. The three branches of the feed pipe 16 each include a shut-off valve that enables each branch to be isolated such that maintenance work can be carried out on a reactor 30 without interrupting the flow of waste oil to the other, still functioning reactors 30.

Each branch of the feed pipe 16 includes upper and lower injection pipes 18. Each upper injection pipe 18 is in fluid communication with the inlet port 32 of the corresponding reactor 30, and each lower injection pipe 18 is in fluid communication with the vertical portion of the corresponding lower circuit pipe 15, such that the injection pipes 18 feed waste oil into the fluid conduit formed by the inlet port 32 and the lower circuit pipe 15. Each injection pipe 18 feeds waste oil horizontally, and hence in a direction that is perpendicular to said fluid conduit, into a portion of said fluid conduit that is offset from its central, ie longitudinal, axis. In this way, waste oil is guided along the curved interior surface of the port 32 or pipe 15, and is hence given an angular momentum, such that a swirling body of waste oil is formed within the fluid conduit formed by the vertical portion of the lower circuit pipe 15 and the inlet port 32.

FIG. 3 is an exploded view of one of the three reactors 30, which are all identical in form. The reactor 30 comprises a cylindrical jacket 33 formed of stainless steel, a microwave window 34 formed in a wall thereof, a reaction chamber in the form of a glass tube 40, and inlet and outlet ports 32,31. The inner surface of the jacket has a highly reflective finish to maximise heating efficiency.

The jacket 33 comprises annular flanges at each end to each of which is fixed an endplate 35,35 a, a gasket 36,36 a being situated between the respective annular flanges and corresponding endplates 35,35 a. Each endplate 35,35 a includes a central circular opening, and the inlet and outlet ports 31,32 of the reactor 30 extend therefrom. The inlet port 32 includes a tangentially-orientated feed port 38 to which the upper injection pipe 18 is connected.

The endplates 35,35 a connect to the jacket 33 using the gaskets 36,36 a and tightening equally spaced nuts and bolts (not shown) that are located around the endplates 35,35 a. A gasket 39 is fitted between the flanged inlet 32 and endplate 35, the two components being secured together by bolts (not shown). A gasket 41 is placed into a rebate (not visible) located on flanged inlet port 32, the reaction chamber, ie glass tube 40, being inserted into the reactor 30 and fitting inside the rebate, on gasket 41. A metal ring 42 and flexible gaskets 43 are placed in position on the glass tube 40. A gasket 44 is placed in position on flanged outlet port 31 and offered up to endplate 35, an inner guiding ring 45 being placed inside the glass tube 40. Flanged inlet port 31 is then bolted to endplate 35 by bolts (not shown).

The glass tube 40 is secured in place by means of tightening bolts 55 (only one of which is shown in FIG. 3) which are housed in tubular projections 56 extending from the flanged outlet 31, and which press the metal ring 42 and flexible gaskets 43 onto the glass tube 40 and gasket 41, creating a gas/liquid/microwave seal. The open ends of the tubular projections 56 are then closed by threaded sealing plugs 57 and sealing rings 58 (again only one of which is shown in FIG. 3), preventing gas, liquid or microwave radiation escaping in the event of the glass tube 40 or gaskets 41,43 failing.

In this way, the reaction chamber (glass tube) 40 is captivated between the inlet and outlet ports 31,32, and extends along the longitudinal axis of the interior of the jacket 33. The upper and lower circuit pipes 15,25 are in fluid communication through the reaction chamber 40 of the reactor 30. The reaction chamber 40 is formed from heat-resistant glass through which high energy microwaves may pass with minimal scattering, and which is sufficiently strong, heat-resistant and durable to withstand the temperatures and pressures generated within the reaction chamber 40 during use. The glass tube 40 is dimensioned such that the microwave energy is “full wave”, thereby maximising heating efficiency.

The jacket 33 also includes an opening in its side wall, and an extension of rectangular cross-section extending therefrom. The microwave window 34, which comprises a frame and a rectangular plate of heat-resistant glass, is mounted to the outer end of the extension. The microwave window 34 is formed such that its longitudinal axis is orientated parallel to the longitudinal axis of the reaction chamber 40.

A waveguide 50 is connected to the microwave window 34, and transmits microwaves from a suitable microwave generator (not shown in the Figures) into the interior of the reactor 30. Currently available microwave generators are capable of producing up to 100 kW microwaves, which is sufficient for the process of the invention, but higher-energy microwaves could be utilised.

In use, collected waste oil is firstly pre-treated to remove excess water and sediment. Appropriate amounts of microwave sensitiser and other additives, such as a catalyst, are added to the waste oil, and then the waste oil is heated using a heat exchanger. The pre-heated waste oil is introduced into the reservoir tank 10 through its inlet port, and is then pre-heated further within the reservoir tank 10.

The variable speed pump 17 is used to withdraw waste oil from the reservoir tank 10, and inject it into the lower circuit pipes 15 and the inlet ports 32 of the reactors 30 so as to create swirling bodies of waste oil. Each swirling body of waste oil is drawn upwards into the reaction chamber 40 of the reactor 30 by a so-called thermal siphon effect. The throughput of waste oil through the tangential inlet 38 may be controlled by appropriate adjustment of the speed of the pump 17. An increase in pump speed may be used in order to remove deposits from the surface of the reaction chamber 40.

Microwaves generated by the microwave generator are transmitted along the waveguides 50, and through the microwave window 34 and the wall of the reaction chamber 40 of each reactor 30. Within the reaction chamber 40 of each reactor 30, the microwaves are finally absorbed by the swirling body of waste oil. Microwaves are prevented from escaping the reactor 30 by an in-line microwave trap (not shown).

In particular, conduction electrons in the microwave sensitiser are accelerated in the oscillating electromagnetic field of the microwaves, creating a discharge of electricity. These discharges of electricity represent a highly non-equilibrium system of ionised molecules and electrons in which the kinetic energy of the electrons is significantly higher than the average temperature of the system. Furthermore, by virtue of the high temperatures that are attained very quickly, the local pressures can also be very high. The electron energy is sufficient to break the chemical bonds within localised areas of the swirling body of waste oil, forming free radicals at substantially lower bulk temperatures than in typical thermal cracking. The other additives act to catalyse or participate in desirable chemical reactions, such as desulphurisation and the removal of other inorganic contaminants.

The major reactions that occur are free radical cracking reactions, as well as hydro-cracking reactions, which are possible by virtue of the high local temperatures and pressures. The swirling movement of the bodies of waste oil ensures that the high local temperatures and pressures that activate the cracking reactions are maintained for only a short period of time before being dispersed in the bodies of waste oil. This reduces the risk of the high temperatures and pressures damaging the apparatus, and in particular rupturing the walls of the reaction chambers 40.

Inorganic contaminants, mainly sulphur and chlorine, react with metals or oxides (added as additives) to form relatively stable compounds such as sulphides and chlorides. Metals, which are present in the collected waste oil by virtue of engine and bearing wear as well as metal containing lubricating oils, either react with sulphur to form sulphides or fall under the action of gravity along the lower circuit pipe 15 into the reservoir tank 10.

The cracking reactions produce a wide range of hydrocarbon products. Vapour, along with entrained liquid droplets and solid particles, flows through the outlet ports 31 of the reactors 30, along the upper circuit pipes 25, into the upper portion of the reservoir tank 10. The entrained liquid droplets and solid particles re-join the waste oil in the reservoir tank 10 to undergo further cracking, and the vapour flows through the outlet port 11 of the reservoir tank 10 into the lower bed of packing in the distillation column 20.

Waste oil that cools before undergoing any cracking, as well as larger solid sediments, will be replaced from below by swirling bodies of waste oil at a higher temperature. The cooler waste oil and solid sediments will therefore fall, under the action of gravity, along the lower circuit pipe 15 into the reservoir tank 10. There will therefore be a continuous flow of waste oil from the reservoir tank 10, through the feed pipe 16, the injection pipes 18 and then the lower circuit pipes 15, back into the reservoir tank 10. This continuous flow maintains the waste oil in a fluid state to ensure the continued functioning of the apparatus.

Solid sediments and other heavy materials, such as carbon, metals and catalyst residue, build up in the lower portion of the reservoir tank 10 during use. This heavy material, commonly referred to as tar, is intermittently drained through the lower outlet port 12 of the reservoir tank 10 in order to ensure that the waste oil within the reservoir tank 10 remains sufficiently fluid to circulate. A conventional auger unit may be used to drain this heavy material.

The vapour that flows into the lower bed of packing is cooled, and a heavy fraction condenses and falls back into the reservoir tank 10. The lighter fraction passes into a middle bed of packing of the distillation column 20. A diesel range liquid product is withdrawn from the bottom of the middle bed, and a naphtha range liquid product is withdrawn from the bottom of an upper bed of packing. Finally, a gaseous product is withdrawn from the top of the distillation column 20.

The rate at which waste oil is fed into the reservoir tank 10 is adjusted so that the level of waste oil within the reservoir tank 10 is maintained substantially constant, and hence the process is continuous.

FIG. 4 shows the general arrangement of the reactor 30 connected to ancillary equipment. Oil is pumped from a holding tank 1 by a pump 3 into the reservoir tank 10 via heat transfer vessel 5. Catalyst held in a catalyst mixing tank 2 is introduced into the system and mixed with oil as it passes through an inline mixer 4. An ultrasonic level gauge (not visible in FIG. 4) controls the oil level in the bottom section of the reservoir tank 10. The oil level in both the reservoir tank 10 and reactor 30 are equal. The ultrasonic level gauge is connected to feed pump 3. The pump 3 starts when the oil falls below a pre-determined level within the reservoir tank 10 and stops when the oil reaches that pre-determined level, creating a thermo-siphon effect. As the oil is heated in the reactor 30 the oil vaporises and exits as a gas.

The gas enters the distillation column 20 and progresses through a gas distributor 29 which evenly distributes the gas as it progresses into the mid section of the distillation column 20. The gas passes through a collection of pall rings 45 that condense approximately 80% of the gas into a diesel fraction. Incondensable gas and lighter oil fractions in the form of gas continue to progress up through the distillation column 20. The diesel fraction exits the distillation column 20 via outlet port 11 and travels through heat transfer unit 5. The hot diesel fraction is cooled in heat transfer unit 5, pre-heating incoming feedstock oil. The diesel fraction is further cooled as it passes through heat transfer unit 60 before it is collected in storage tank 61.

The diesel fraction can be pumped back into the midsection of the distillation column 20 by a recirculation pump 62, through a spray nozzle. The spray helps condense the diesel fraction. Gas progresses into the top section of the distillation column 20, where a naphtha fraction is condensed. Uncondensed gas exits the top of the distillation column 20 and is transferred into a gas condensing unit 63 where waste water is removed. Gas exits the gas condensing unit 63 and is stored in gasholder 64. In the event of pressure build up, gas can be flared off by a ground flare 65.

The naphtha fraction exits the distillation column 20 via outlets 66, and is cooled in heat transfer unit 67 before being stored in storage tank 68.

The carbon coke, heavy particulates, spent catalyst and heavy ends are allowed to build up in the bottom of the tank 10 until they reach a vibrating level probe 70. The probe 70 senses the sediment level and activates a remote warning light, whereupon the waste is removed from the distillation column 20 using an auger unit 71.

FIG. 5 shows an alternative, and presently preferred, reactor 130 that differs in several respects from the reactor 30 shown in FIG. 3. In particular, this alternative reactor 130 includes a catalytic rod 200 that extends along a central axis of the reaction chamber 140. The catalytic rod 200 is mounted at its ends within the inlet and outlet ports 131,132 of the reactor 130.

The outlet port 131 includes a support 184 and a turbine rotor 186, which are shown in FIGS. 5 and 6. The support 184 comprises a central pillar that is mounted at each end between a pair of radial struts that extend from the interior surface of the outlet port 131, so that the central pillar extends along a central axis of the outlet port 131. The central pillar of the support 184 includes a recess at its lower end for receiving the upper end of the catalytic rod 200, as shown most clearly in FIG. 5.

The turbine rotor 186 is rotatably mounted about the central pillar of the support 184, and comprises a plurality of blades that are arranged such that the turbine rotor 186 entirely occludes the outlet port 131 along axial directions, but defines openings through which material may flow during use. The turbine blades are electrically conductive, and hence this arrangement prevents the escape of microwave radiation from the reaction chamber 140, during use. Furthermore, material flowing through the outlet port 131 will impinge upon the turbine rotor 186, and hence impart a rotational force thereon, during use. In this embodiment of the apparatus according to the invention the rotation of the turbine rotor 186 may therefore be monitored, and the output rate of the reactor 130 thereby calculated.

The inlet port 132 includes a support 194 for the catalytic rod, which is shown in FIGS. 5 and 7. The support 194 comprises three radial turbine blades 196 extending from a central hub 198, the central hub 198 having a cylindrical upper portion with a recess at its upper end for receiving a lower end of the catalytic rod 200 and a conical lower portion. The turbine blades 196 extend radially between the interior surface of the inlet port 132 and the central hub 198, and together define three openings through the inlet port 132 of equal size. Furthermore, the turbine blades 196 are arranged so that material flowing through the inlet port 132 into the reaction chamber, during use, impinges upon those blades 196 and is deflected transversely in the same direction as that in which the material is swirling. In this way, the turbine blades 196 do not occlude a large proportion of the inlet port 132, and hence offer low resistance to flow, but facilitate formation of a swirling body of material within the reactor chamber 140.

As shown in FIGS. 5 and 8, the catalytic rod 200 extends along a central axis of the reactor chamber 140 between the supports 184,194 of the inlet and outlet ports 131,132. The catalytic rod comprises carbon, and acts to catalyse the cracking reactions that occur within the reaction chamber 140.

In all other respects, the alternative reactor 130 shown in FIG. 5 is identical to the reactor shown in FIG. 3. 

1. A process for refining waste oil, the process comprising transferring waste oil from a reservoir tank into a reaction chamber such that a swirling body of waste oil is formed within the reaction chamber, and exposing the swirling body of waste oil to microwave radiation such that cracking reactions occur, wherein waste oil that cools within the reaction chamber before undergoing any cracking is replaced from below by swirling bodies of waste oil at a higher temperature, and the cooler waste oil falls, under the action of gravity, along a circuit conduit into the reservoir tank.
 2. A process as claimed in claim 1, wherein waste oil is transferred by one or more injection conduits from a reservoir tank either directly into the reaction chamber, or into the circuit conduit that communicates with the reaction chamber, such that a swirling body of waste oil is formed within the reaction chamber.
 3. A process as claimed in claim 2, wherein a swirling body of waste oil is formed within the circuit conduit, which communicates with an opening in a lower part of the reaction chamber, and this swirling body rises by thermal effects into the reaction chamber.
 4. A process as claimed in claim 3, wherein the waste oil is guided by the one or more injection conduits into a portion of the circuit conduit that is offset from its central, longitudinal axis, along a direction that is orientated transversely to that axis.
 5. A process as claimed in claim 1, wherein as the cracking reactions refine the waste oil and the products are removed, the waste oil is replenished within the reservoir tank so as to maintain the level of waste oil within the reservoir tank substantially constant.
 6. A process as claimed in claim 1, wherein the waste oil is heated before being introduced into the reservoir tank, and is heated further within the reservoir tank.
 7. A process as claimed in claim 1, wherein a microwave radiation sensitiser is added to the waste oil before it is transferred to the reaction chamber.
 8. A process as claimed in claim 7, wherein the sensitiser is added to the waste oil before it is introduced into the reservoir tank.
 9. A process as claimed in claim 8, wherein other additives are also added to the waste oil before it is introduced into the reservoir tank.
 10. A process as claimed in claim 1, wherein the circuit conduit extends from an opening in the lower part of the reaction chamber to a port in a lower portion of the reservoir tank.
 11. A process as claimed in claim 1, wherein solid sediments and other heavy materials build up in a lower portion of the reservoir tank, and this heavy material is intermittently drained through an outlet port in the base of the reservoir tank.
 12. A process as claimed in claim 1, wherein a catalytic substrate is situated within the reaction chamber during exposure of the swirling body of material to microwave radiation.
 13. A process as claimed in claim 1, wherein the reaction chamber is housed within an electrically-conductive jacket, with an inert gas-filled space separating the reaction chamber from the wall of the jacket, and microwave radiation enters the jacket through a window, before entering the reaction chamber to be absorbed by the swirling body of waste oil.
 14. A process as claimed in claim 13, wherein the entire reaction chamber is exposed to microwave radiation.
 15. A process as claimed in claim 13, wherein a waveguide transmits the microwave radiation from a source to the window of the jacket.
 16. A process as claimed in claim 1, wherein vapour products, and also any entrained liquid droplets and solid particles, escape from the reaction chamber through an upper opening of the reaction chamber.
 17. A process as claimed in claim 16, wherein the vapour products, and any entrained liquid droplets and solid particles, passing through the upper opening of the reaction chamber are transferred to an upper portion of the reservoir tank where the entrained liquid droplets and solid particles are returned to the waste oil.
 18. A process as claimed in claim 17, wherein the vapour products flow into a product recovery apparatus through an upper outlet port of the reservoir tank.
 19. An apparatus for refining waste oil, the apparatus comprising a reservoir tank, at least one injection conduit configured to transfer the waste oil from the reservoir tank into the reaction chamber such that a swirling body of waste oil is formed within the reaction chamber, in use, and a source of microwave radiation adapted to expose the swirling body of waste oil to microwave radiation such that cracking reactions occur, wherein the apparatus is adapted such that waste oil that cools, in use, within the reaction chamber before undergoing any cracking is replaced from below by swirling bodies of waste oil at a higher temperature and the cooler waste oil falls, under the action of gravity, along a circuit conduit into the reservoir tank.
 20. An apparatus as claimed in claim 19, wherein the swirling body of waste oil is created within the reaction chamber by the one or more injection conduits that transfer waste oil from a reservoir tank either directly into the reaction chamber, or into the circuit conduit that communicates with the reaction chamber, such that a swirling body of waste oil is formed within the reaction chamber.
 21. An apparatus as claimed in claim 20, wherein the one or more injection conduits are adapted to guide the waste oil into a portion of the circuit conduit that is offset from its central, longitudinal axis, along a direction that is orientated transversely to that axis.
 22. An apparatus as claimed in claim 20, wherein the reaction chamber is cylindrical, with open upper and lower ends, and is orientated generally vertically.
 23. An apparatus as claimed in claim 22, wherein the portion of the circuit conduit that is immediately below the reaction chamber is orientated vertically, and the injection conduits are adapted to feed the waste oil into the circuit conduit in a generally horizontal direction.
 24. An apparatus as claimed in claim 23, wherein the open lower end of the reaction chamber is in sealed communication with the circuit conduit, and has an internal diameter that matches the internal diameter of the circuit conduit.
 25. An apparatus as claimed in claim 19, wherein the entire wall of the reaction chamber is formed from a heat-resistant glass.
 26. An apparatus as claimed in claim 19, wherein the circuit conduit extends from an opening in the lower part of the reaction chamber to a port in a lower portion of a reservoir tank.
 27. An apparatus as claimed in claim 19, wherein a catalytic substrate is situated within the reaction chamber.
 28. An apparatus as claimed in claim 27, wherein the catalytic substrate comprises carbon as a catalyst.
 29. An apparatus as claimed in claim 28, wherein the catalytic substrate has the form of a rod that extends along a central axis of the reaction chamber.
 30. An apparatus as claimed in claim 27, wherein the catalytic substrate is mounted at its ends, with the mountings being situated within inlet and outlet ports for the reaction chamber.
 31. An apparatus as claimed in claim 30, wherein each of the mountings comprises a central hub for receiving an end portion of the catalytic substrate, and a plurality of radial support struts.
 32. An apparatus as claimed in claim 31, wherein the radial support struts in the inlet port have the form of deflector blades, the deflector blades being adapted to deflect waste oil flowing into the reaction chamber transversely relative to the longitudinal axis of the reaction chamber so as to facilitate formation of a swirling body of waste oil.
 33. An apparatus as claimed in claim 19, wherein a microwave barrier is disposed within an outlet port for the reaction chamber, and the microwave barrier comprises one or more electrically conductive members configured to prevent escape of microwave radiation from the reaction chamber through the outlet port.
 34. An apparatus as claimed in claim 33, wherein the microwave barrier has the form of a turbine rotor that is adapted to be rotated by material exiting the reaction chamber through the outlet port.
 35. An apparatus as claimed in claim 34, wherein the apparatus includes means for monitoring the rotation of the turbine rotor, and means for calculating therefrom the rate of flow through the outlet port.
 36. An apparatus as claimed in claim 19, wherein the reaction chamber is housed within an electrically-conductive jacket.
 37. An apparatus as claimed in claim 36, wherein the reaction chamber is mounted co-axially within a cylindrical jacket, with an inert gas-filled space separating the reaction chamber from the wall of the jacket.
 38. An apparatus as claimed in claim 37, wherein the jacket includes a window through which microwave radiation is able to enter the jacket, before entering the reaction chamber to be absorbed by the swirling body of waste oil.
 39. An apparatus as claimed in claim 38, wherein the window is dimensioned and configured such that the entire reaction chamber is exposed to microwave radiation.
 40. An apparatus as claimed in claim 38, wherein the apparatus includes a waveguide that transmits the microwave radiation from a source to the window of the jacket.
 41. An apparatus as claimed in claim 19, wherein the apparatus includes means for separating the products of the cracking reactions.
 42. An apparatus as claimed in claim 41, wherein the reaction chamber has an upper opening through which vapour products, and also any entrained liquid droplets and solid particles, are able to escape from the reaction chamber.
 43. An apparatus as claimed in claim 42, wherein the apparatus is adapted such that the vapour products, and any entrained liquid droplets and solid particles, passing through the upper opening of the reaction chamber are transferred to an upper portion of the reservoir tank where the entrained liquid droplets and solid particles are returned to the waste oil.
 44. An apparatus as claimed in claim 43, wherein the reservoir tank includes an upper outlet port through which the vapour products are able to flow into a product recovery apparatus. 